A vehicle (e.g., car, plane, truck, boat, etc.) can include a fluid-flow control system. The fluid-flow control system can direct fluid flow in a particular manner. Examples of a fluid can include a liquid or gas, such as air. The fluid-flow control system can include a fan for directing the fluid flow. In some cases, the fan can direct fluid flow in the direction that the fan is facing. For example, the fan may blow air in a forward direction if the fan is facing forwards and in a backward direction if the fan is facing backwards. In other cases, the fan can direct fluid flow in the same direction either way. For example, the fan may blow air in a forward direction, regardless of whether the fan is facing forwards or backwards. This may be due to the shape of the fan's blades.
Fans that direct fluid flow in the same direction either way may operate with higher efficiency if the fan is oriented facing one direction than if the fan is oriented facing the opposite direction. For example, the fan may blow more air in the forwards direction if the fan is facing forwards than if the fan is facing backwards. So, it may be desirable to orient the fan facing in a particular direction in a fluid-flow control system to improve the efficiency and performance of the fluid-flow control system. But such fans may be mistakenly installed backwards (e.g., facing the opposite direction), since both sides of the fan may look visually similar and the fan blows in the same direction either way.